The present invention relates to a cutting portion for a drill bit.
U.S. Pat. No. 3,888,320 A discloses a cutting portion that is connectable to a drill bit via a detachable plug-and-twist connection to a drill shaft portion. The drill bit is attached in the tool receptacle of a core drilling device and, during drilling, driven by the core drilling device in a rotational direction around an axis of rotation. The cutting portion comprises an annular portion, a plurality of cutting elements connected on a first end to the annular portion, and an outer insertion element that is connected on a second end facing away from the cutting elements to the annular portion. The drill shaft portion comprises a cylindrical drill shaft having an inner insertion element on one end facing the cutting portion. The inner and outer insertion elements form a plug connection in an insertion direction parallel to the axis of rotation. The outer insertion element comprises a plurality of pin elements on its interior that are directed radially inward in a plane perpendicular to the axis of rotation. The inner insertion element comprises a plurality of slit-shaped clearances in the shape of an L into which the pin elements are inserted. The L-shaped clearances comprise a transverse slit running perpendicular to the axis of rotation and a connector slit that runs parallel to the axis of rotation and connects the transverse slit to a lower edge of the inner insertion element. The insertion element of the drill shaft portion is designed in an open fashion in the region of the connector slits. The pin elements that are attached to the cutting portion are inserted via the connector slit.
One disadvantage of the known cutting portion may be seen when the cutting portion has become jammed in the substrate. In core drilling, it is common for the cutting section to become jammed in the substrate during drilling and need to be removed by the operator. In stand-guided core drilling devices, in order to remove a jammed cutting section, the drill bit is driven opposite the rotational direction and the drill stand exerts a tensile force on the drill bit directed opposite the drilling direction. The operator attempts to free the cutting portion from the substrate by manually rotating it with the aid of a tool key and, at the same time, pulling with the aid of the drill stand. The L-shaped clearances of the known cutting portion present the risk that the operator will rotate the drill shaft portion around the axis of rotation until the pin element comes into contact with the connector slit and, at the same time, operate the handwheel of the drill stand, such that the pin element is moved out of the connector slit. As soon as the plug-and-twist connection between the cutting portion and the drill shaft portion has been opened, the cutting portion must be freed from the substrate in another manner, for example, by the removal of the substrate.
The object of the present invention is to develop an exchangeable cutting portion for a drill bit in which the risk is reduced of the connection accidentally being opened during the removal of a jammed drill bit from the substrate and the drill shaft portion being removed from the substrate without the cutting portion. In addition, the stability of the cutting portion during drilling and the ability of the cutting portion to withstand tensile force exerted by a drill stand should be increased.
Provision is made according to the invention for the insertion element to comprise at least one slit-shaped clearance having a transverse slit and a connector slit, with the transverse slit being disposed perpendicular to the axis of rotation and being connected via the connector slits to an upper edge of the insertion element. The insertion element of the cutting portion is designed in an open fashion in the region of the connector slits. The pin elements that are attached to the drill shaft portion are inserted via the connector slit; the connector slit may be disposed parallel or at an oblique angle to the axis of rotation. The transmission of torque from the pin elements to the plug element occurs in the transverse slit.
The drill bit segments comprising the slit-shaped clearances is more susceptible to deformation by tensile force than the drill bit segment to which the pin elements are attached. The arrangement of the slit-shaped clearances on the exchangeable cutting portion has the advantage that the less stable drill bit segment is exchanged. The cutting portion according to the invention has a higher degree of stability and ability to withstand tensile force.
It is preferable for the insertion element to comprise three or more slit-shaped clearances. Here, the slit-shaped clearances are preferably evenly distributed around the axis of rotation of the cutting portion. Due to the even distribution of the slit-shaped clearances, it is not necessary to assign pin elements to clearances, and a pin element may be inserted into any clearance.
In a preferred embodiment, the insertion element has an outer and inner diameter perpendicular to the axis of rotation and extends parallel to the axis of rotation over a length. The annular insertion element allows the formation of a plug connection with an inner insertion element and an outer insertion element. The inner insertion element is preferably provided on the drill shaft portion and the outer insertion element on the cutting portion. Due to the arrangement of the slit-shaped clearances on the outer insertion element and the arrangement of the pin elements on the inner insertion element, the drill bit can be designed in a watertight fashion on the inside and the misdirection of a cooling and rinsing medium can be prevented. When a drill bit is watertight, all of the cooling and rinsing medium is supplied, for example, via the insertion end of the drill bit, to the work surface and ensures the cooling of the cutting elements and the removal of drillings. The cutting portion according to the invention also allows the operator to monitor the opening and closing of the plug-and-twist connection. This monitoring is not possible or is possible only to a limited degree if the slit-shaped clearances are provided on the inner insertion element.
It is particularly preferred for the length of the insertion element to be at least 18 mm. At a minimum length of 18 mm for the insertion element, sufficient ability to withstand force is ensured for the cutting portion. The slit-shaped clearances may be positioned on the insertion element at such a height that the cutting portion is able to withstand tensile forces that occur during the removal of a jammed drill bit with the aid of a drill stand.
Here, it is particularly preferred for the length of the insertion element not to exceed 28 mm. Up to an insertion element length of 28 mm, the ability of the insertion element to withstand tensile force is improved. Greater insertion element lengths have no or very little influence on the ability of the cutting portion to withstand tensile force and only incur increased material and manufacturing costs.
It is preferable for the transverse slit parallel to the axis of rotation to have a lower distance from the annular portion of at least 3 mm. A minimum distance of 3 mm guarantees a sufficient ability on the part of the cutting portion to withstand tensile force during the removal of a jammed drill bit with the aid of a drill stand.
Here, it is particularly preferred for the lower distance from the transverse slit to the annular portion not to exceed 5 mm. Up to a distance of 5 mm, the ability of the cutting portion to withstand tensile force is improved. Greater distances have no or very little influence on the ability of the cutting portion to withstand tensile force and only incur increased material and manufacturing costs.
In a refinement of the cutting portion, the transverse slit comprises a catching region and a locking region, with the catching region being connected to the connector slit on a side of the connector slit facing the rotational direction and the locking region being connected to the connector slit on a side of the connector slit opposite the rotational direction. The transmission of torque from the drill shaft portion onto the cutting portion occurs via the pin elements and the catching region. The locking region is disposed on the side of the connector slit opposite the catching region. The locking region reduces the risk of the plug-and-twist connection between the drill shaft portion and the cutting portion being unintentionally opened during the release of a jammed cutting portion from the substrate. The operator attempts to free the jammed cutting portion from the substrate by rotating the drill shaft portion around the axis of rotation with the aid of a tool key and, at the same time, pulling it with the aid of the drill stand. Practical experience has shown that operators primarily pull on the drill shaft portion when the pin element is resting against the transverse slit. When the pin element is resting against the catching region or the locking region, there is no risk that the plug-and-twist connection will be opened. In the cutting portion according to the invention, the plug-and-twist connection will be opened only if the operator pulls on the drill shaft portion at the precise moment at which the pin element is located over the connector slit. The risk of unintentionally opening the plug-and-twist connection is considerably reduced as compared to slit-shaped clearances in the shape of an L.
In a first preferred variant, the width of the catching region and the width of the locking region coincide. Here, the catching region and locking region preferably have a minimum width of the pin radius plus 1.5 mm and a maximum width of the pin radius plus 3 mm. This embodiment is particularly advantageous for cutting portions with large diameters, in which the proportion of the circumference occupied by transverse slits is small.
In a second preferred variant, the width of the catching region is greater than the width of the locking region. Here, the catching region and the locking region preferably have a minimum width of the pin radius plus 1.5 mm and a maximum width of the pin radius plus 3 mm. This embodiment is particularly advantageous for cutting portions with small diameters, in which the proportion of the circumference occupied by transverse slits is large.
It is preferred for the height of the connector slit parallel to the axis of rotation of the cutting portion to be at least 10 mm. At a height of at least 10 mm, sufficient ability by the cutting portion to withstand tensile force exerted by a drill stand is ensured.
Here, it is particularly preferred for the height of the connector slit parallel to the axis of rotation not to exceed 13 mm. Up to a height of 13 mm, the ability of the cutting portion to withstand tensile force exerted by a drill stand is improved. Greater heights have no or very little influence on the ability of the cutting portion to withstand tensile force exerted by a drill stand and only incur increased material and manufacturing costs.
In a refinement of the cutting portion, the annular portion comprises a guide portion, with the guide portion being flush to an outer edge, an inner edge, or to an outer edge and an inner edge of the cutting elements parallel to the axis of rotation. Due to the flush connection of the guide portion to the cutting elements, the guide portion forms a guide for the cutting elements during drilling and stabilizes the cutting elements. Here, guidance may occur on the outside of the cutting portion via the substrate surrounding the drill bore or on the inside of the cutting portion via the drill core.
It is preferable for the length of the guide portion parallel to the axis of rotation to be less than 4 mm. A guide portion that is less than 4 mm does not impede the supply of a cooling and rinsing medium, or does not do so to a substantial degree.
In a preferred embodiment of the cutting portion, the outer insertion element comprises a groove disposed in the axial direction at the height of the slit-shaped clearances. An “axial direction” is defined as a direction parallel to the axis of rotation of the cutting portion. The groove can form a positive connection in the axial direction with a nose attached on the inner insertion element of a drill shaft portion. Due to the additional positive connection between the drill shaft portion and the cutting portion, the risk of the detachable connection between the drill shaft portion and the cutting portion being unintentionally opened during the removal of a jammed drill bit from the substrate is further reduced.
Sections result between the slit-shaped clearances of the outer insertion element that display an elastic effect. The elastic effect may be adjusted via the number and axial height of the slit-shaped clearances and the length of the outer insertion element. In order to separate the drill shaft portion from the cutting portion, a force is exerted in the axial direction on the face of the outer insertion element with the aid of a tool. Due to the effect of the force, the elastic portion of the outer insertion element is deflected and the positive connection between the nose and the groove can be released.
It is particularly preferred for the groove to be annular in shape and disposed in a plane perpendicular to the axis of rotation. A groove with an annular design disposed at the height of the slit-shaped clearances supports the elastic effect of the portions of the outer insertion element between the slit-shaped clearances.
Exemplary embodiments of the invention will be described in the following with reference to the drawings. The drawings are not necessarily intended to show the exemplary embodiments to scale; rather, the drawings are shown in a schematic and/or slightly distorted manner when it aids understanding to do so. With regard to elaborations on the teachings immediately discernible from the drawings, we refer to the relevant prior art. It should be noted here that numerous modifications and alterations may be made regarding the form and details of an embodiment without deviating from the general concept of the invention. The features of the invention disclosed in the specification, the drawings, and the claims may be considered essential to the refinement of the invention either alone or in any combination. In addition, all combinations of at least two features disclosed in the specification, the drawings, and/or the claims may be considered to fall within the scope of the invention. The general concept of the invention is not limited to the exact form or details of the exemplary embodiment shown and described in the following or limited to an object that would be considered limited in comparison to the object disclosed in the claims. In the case of measurement ranges given, values lying within the ranges named as boundary values should also be considered claimed and usable in any desired manner. For the sake of simplicity, the same reference characters have been used in the following for identical or similar parts or parts with an identical or similar function.